The conventional face masks on football helmets provide good protection against injury to the mouth, teeth and nose of the wearer. Ironically, however, they do create some risk of injury to the wearer's neck: if another player grips the mask and jerks it abruptly, the mask can act as a lever to increase the twisting force on the neck, and thereby can cause an injury which might not otherwise occur, or can increase its seriousness. (For this reason the penalty in football for a "face mask" violation is a relatively severe assessment of 15 yards.)